1. Field of the Invention
The present invention relates to a chemical mechanical polishing slurry for semiconductor integrated circuit manufacturing and, more particularly, to improved chemical mechanical polishing slurries for polishing metal layers and thin-films used in semiconductor integrated circuit manufacturing.
2. Background of the Related Art
A semiconductor wafer typically includes a substrate, such as a silicon or gallium arsenide wafer, on which a plurality of transistors have been formed. Transistors are chemically and physically connected into a substrate by patterning regions in the substrate and layers on the substrate. The transistors are interconnected through the use of well known multilevel interconnects to form functional circuits. Typical multilevel interconnects are comprised of stacked thin-films consisting of one or more of the following: titanium (Ti), titanium nitrite (TiN), tantalum (Ta), aluminum-copper (Al--Cu), aluminum silicon (Al--Si), copper (Cu), tungsten (W), and various combinations thereof.
The traditional technique for forming interconnects has been improved by the disclosure of U. S. Pat. No. 4,789,648 to Chow et al. relating to a method for producing coplanar multilevel metal/insulator films on a substrate. This technique, which has gained wide interest and produces multilevel interconnects, utilizes chemical mechanical polishing (CMP) to planarize the surface of the metal layers or thin-films during the various stages of device fabrication. In general, CMP involves the concurrent chemical and mechanical polishing of an overlying first layer to expose the surface of a non-planar second layer on which the first layer is formed. One such process is described in U. S. Pat. No. 4,789,648 to Beyer et al., the specification of which are incorporated herein by reference. Briefly, Beyer et al. discloses a CMP process using a polishing pad and a slurry to remove a first layer at a faster rate than a second layer until the surface of the overlying material becomes coplanar with the upper surface of the initially covered second layer. For a more detailed explanation of chemical mechanical polishing, please see U. S. Pat. Nos. 4,671,851, 4,910,155 and 4,944,836, the specifications of which are incorporated herein by reference.
Polishing slurry composition is an important factor in providing a manufacturable chemical mechanical polishing process. Typical polishing slurries available for CMP processes contain an abrasive such as silica or alumina in an acidic or basic solution. For example, U. S. Pat. No. 4,789,648 to Beyer et al. discloses a slurry formulation using alumina abrasives in conjunction with sulfuric, nitric, acetic acids and deionized water. Similarly, U. S. Pat. No. 5,209,816 to Yu et al. discloses a slurry for polishing aluminum using alumina abrasives in conjunction with phosphoric acid, hydrogen peroxide, and deionized water. U. S. Pat. Nos. 5,391,258 and 5,476,606 to Brancaleoni et al. discloses a slurry for polishing a composite of metal and silica which includes an aqueous medium, abrasive particles and an anion which controls the rate of removal of silica. The anion contains at least two acid groups and the pKa of the first dissociable acid is not substantially larger than the pH of the polishing slurry, wherein the term substantially is defined as 0.5 units.
Other polishing slurries for use in CMP processes are described in U. S. Pat. No. 5,354,490 to Yu et al., U. S. Pat. No. 5,340,370 to Cadien et al., U. S. Pat. No. 5,209,816 to Yu et al., U. S. Pat. No. 5,157,876 to Medellin, U. S. Pat. No. 5,137,544 to Medellin, and U. S. Pat. No. 4,956,313 to Cote et al., the specifications of which are incorporated herein by reference.
Although many of the slurry compositions are suitable for limited purposes, the slurries described above tend to produce poor film removal traits for the underlying films or produce deleterious film-corrosion which leads to poor manufacturing yield of typical multilevel metallization structures. In addition, the polishing slurries tend to exhibit unacceptable polishing rates and corresponding selectivity levels to the insulator media.
Accordingly, a need remains for improved polishing slurries and processes related thereto which provide uniform metal layers and thin-films, free from undesirable contaminants and surface imperfections. In particular, it is highly desirous to produce a polishing slurry for multilevel interconnects having low selectivity to the barrier films, e.g., Ti, TiN, Ta, and high selectivity to the insulator media surrounding the multilevel interconnects, e.g., silica, spin on glass, and low-k dielectric materials, which are not hazardous or corrosive. A further need remains for a single slurry which is capable of providing both the low selectivities and high selectivities to the barrier and insulator films, respectively.